A wound rotor type generator and an induction motor conventionally have been used as a rotary electric machine used for a railway rolling stock. However, in these days, instead of them, as high performance and cost reduction of permanent magnets and wide spreading of high performance inverter are realized, a trend of employing a permanent magnet type electric rotary machine is increasing since the permanent magnet type electric rotary permits to reduce size and weight thereof as well as to realize a high efficiency.
In such a situation, in order to improve an electric characteristic and a mechanical strength characteristic of the rotary electric machine, rotor structures using variety types of permanent magnets have been investigated.
For example, Patent Document 1 (JP-A-2006-333656) discloses a structure in which permanent magnets are buried in respective permanent magnet slots formed inside a rotor core, and the adjacent slots in which the permanent magnets are buried are disposed so as to constitute nearly an inverted obtuse V shape when seeing them a rotor shaft side. In addition, the structure has a bridge portion being provided in between respective adjacent slots (each two slots) so as to connect a salient pole portion forming the outer side of the slots to the inner side central portion. Patent Document 2(JP-A-2004-260888) discloses a structure in which a plurality of slots are formed along the circumferential direction of a rotor in an adjacent manner, permanent magnets are buried in the respective slots, and the sides at both ends in the circumferential direction of the respective slots are respectively slanted and the connection part with the other side thereof is formed in an circular portion.
By employing these structures, stress concentration acting on between the adjacent slots can be avoided.
Incidentally, in the case of a rotary electric machine used for a railway rolling stock, since the weight thereof greatly affects to riding comfort of the railway rolling stock, it becomes a key point to reduce the weight of the rotary electric machine. Particularly, with respect to a large capacity rotary electric machine of a class having an output of several hundreds kW˜several MW, as the physical size of the rotary electric machine becomes larger, there is occurred specific problems to a large capacity machine become remarkable. That is, in the rotor structure of a rotary electric machine, in view of an easy assembling and reduction of number of parts, frequently employed structure is such that permanent magnet slots are provided for a rotor core and permanent magnets are buried in the permanent magnet slots. A disadvantage of this structure is such that the electric characteristic and the mechanical strength characteristic are in a trade-off relationship depending on the structure of the permanent magnet slots and the position thereof inside the rotor.
As the size of a rotary electric machine increases, the centrifugal force of the rotor increases, therefore, it is required to have a mechanical strength enduring such centrifugal force, to ensure reliability and to satisfy a specified electric characteristic. Further, as the rotary machine upsizes, the amount of material to be used increases, therefore, in view of the cost reduction, it is desired to reduce the amount of magnet to be used and to use low cost materials.
As has been explained above, Patent Document 1 discloses a structure in which the slots where the permanent magnets are buried are disposed so that the respective adjacent slots form in nearly an inverted obtuse V shape when seeing them from a rotor shaft side and respective rest-core portions between the adjacent slots are formed in the rotor core, and the permanent magnet for each of poles is divided into four.
However, according to such a structure, in the rotor core, since the width of each of the rest core-portions between the adjacent slots (adjacent permanent magnet slots) and the position (in radial and circumferential directions) of the permanent magnets etc. are not specified, in particular, with respect to a large scaled rotary electric machine having a large capacity, in accordance with increases of circumferential velocity and of an amount of permanent magnet to be used, the centrifugal force also increases, accordingly, the consideration on both mechanical strength and electrical characteristics may be insufficient.
On the other hand, Patent Document 2 discloses a structure in which a permanent magnet constituting one pole is divided into five, all of the divided permanent magnets are disposed in parallel in a manner with no steps and at both end portions of a permanent magnet slot a curved portion and a slanted portion are provided.
However, with the structure of patent document 2, since the permanent magnets are disposed in parallel in the circumferential direction with no steps, great difference is caused in distances from the respective permanent magnet slots to the outer circumference of the rotor, the weight of the iron core increases depending on the corresponding length of the distance from the respective permanent magnet slots to the outer circumference of the rotor, and the centrifugal force also increases. Therefore, since such as the width of the respective rest-core portions between the adjacent slots and the configuration of the curved portions at the end portions of respective permanent magnet slots are the same, it is difficult to relax stress concentration relating to fatigue strength.